The invention relates to an improved tooth displacement measuring apparatus and, more particularly, to such an apparatus including circuitry adapted to provide an automatic zero-displacement adjustment for measured values of tooth displacement and for storing and later displaying measured values of tooth displacement corresponding to particular values of applied force.
When examining the condition of teeth, it is often useful to determine the degree of movement of individual teeth in response to applied force, since the degree of loosening of a tooth provides an indication of the existence of or the extent of the decay of the tooth-accomodating bone and of the tooth-supporting structure. Accordingly, tooth displacement measuring devices have been devised to apply increasing pressure on the tooth under examination and to measure the resulting relative displacement of the tooth with respect to adjacent teeth.
More particularly, devices employing three calipers or measuring rods are known to the art. In such devices, a force transmitting rod is supported within a housing by a force spring. The rod extends outside of the housing and its free end is adapted to be attached to a test tooth. Two displacement measuring rods are typically positioned adjacent the force transmitting rod and are supported within the housing by respective weak restoring springs that are adapted to apply a weak counter restoring force in response to axial forces applied to the rods.
In operation, the free end of the force transmitting rod is affixed to the test tooth and the ends of the displacement measuring rods are positioned to abut adjacent teeth. The housing is then pressed manually in a forward direction and the force transmitting rod is thereby caused to apply increasing pressure on the test tooth.
The applied force is measured by a force transducer that is attached to the force transmitting rod. The transducer is typically used to measure the force acting upon the force spring.
As pressure is applied to the test tooth, position sensing transducers on the displacement measuring rods register the relative displacement between the respective displacement rods and the force transmitting rod.
Thus, such a prior art device is adapted to measure the relative displacement of a test tooth with respect to adjacent reference teeth in response to applied force.
However, in order to display the force and displacement measurements taken by such prior art devices, it has been necessary to utilize a relatively complicated twinchannel recorder that plots curves corresponding to the applied force and the resultant tooth displacement. Typically, the data plots are then used to prepare a force-displacement graph that describes the displacement characteristics of the tooth. Such an analysis of the tooth displacement data is not only expensive and time consuming but is also better adapted to use in scientific institutions than in a dentist's office.
It has been suggested that the tooth displacement data analysis may be simplified by plotting the displacement curve and superimposing on this curve the peaks that arise when the force acting on the tooth is increased by a particular amount. However, it has been determined that the evaluation of even such a simplified curve is a tedious operation that would probably not be suitable to a practicing dentist.
In addition, a further disadvantage of the prior art is that a displacement measuring device must be adjusted to a zero displacement reading after it is engaged with the test tooth and reference teeth, since the displacement measuring rods will initially be deflected slightly from their zero force positions, even though no force is being exerted on the test tooth.
It should be appreciated that not only is such an initial calibration adjustment time consuming, but also the adjustment is difficult to execute since the housing of the device must be held very steadily to avoid additional movement of the displacement rods.
Practical tests have shown that a satisfactory, quantitative evaluation of tooth displacement may be obtained if tooth displacement is measured at particular values of applied force. For example, it has been determined that it is sufficient to measure tooth displacement at forces of 100 pond and 500 pond applied perpendicular to the axis of the tooth and in both the palatal or compression stress and labial or tensile stress directions.
Accordingly, it is an object of the invention to provide a simple and effective means to measure tooth displacement in response to particular values of applied force.
A further object of the invention is to provide an apparatus to automatically apply a zero displacement adjustment to measured values of displacement.
Another object of the invention is to provide a simple means to store and display measured displacement values.
These and other objects of this invention will become apparent from a review of the detailed specification which follows and a consideration of the accompanying drawings.